This invention relates to microelectronic fabrication systems, and more particularly to methods and systems for cleaning microelectronic fabrication systems.
Microelectronic fabrication systems are widely used to fabricate microelectronic devices such as microelectronic wafers, integrated circuits and liquid crystal display panels. Tile environment of a microelectronic fabrication process generally must be maintained in a very clean state, in order to allow high yields of microelectronic devices. In general, as microelectronic devices become more highly integrated, a higher degree of cleanness may be required.
A unit process region where a specific process is performed on a microelectronic substrate such as a wafer, generally includes a wafer process area where a predetermined operation is performed on the wafer and a wafer transfer area where the wafer is loaded/unloaded to/from the wafer process area. The unit process region is located in a service area of the microelectronic fabrication system
The unit process region generally adjoins a working area which is also referred to as a bay. After a boat having wafers mounted thereon is moved from the working area to the wafer transfer area by an operator, a robot in the wafer transfer area loads wafers one by one from the boat to the wafer process area. The robot in the water transfer area also performs an unloading operation of wafers from the wafer process area, after processing has been performed.
FIGS. 1 and 2 are a top view and a side view of a layout of a conventional microelectronic fabrication system.
In FIGS. 1 and 2, reference numeral 1 denotes a clean room that is isolated from the outside environment and that includes a working area 10 and a service area 20. In the clean room 1, the temperature and the humidity are controlled and particle-removed clean air flows downward.
An upper plenum 2 for supplying clean air is placed in the upper portion of the clean room 1, and a lower plenum 3 for recovering the air that passes through the clean room 1 is placed in the lower portion thereof. The clean air supplied from the upper plenum 2 passes through the working area 10 and the service area 20 via a filter. Fine particles generated in the working area 10 and in the service area 20 are exhausted through the lower plenum 3 that is maintained at a low pressure, together with the clean air.
The clean room 1 is maintained at a pressure higher than the atmospheric pressure so that external air is not induced inside. Also, the pressure of the working area 10 is adjusted to be higher than that of the service area 20. This can prevent the fine particles generated in the service area 20 from being induced into the working area 10, due to the pressure difference. The pressure difference is controlled by adjusting the amount and/or velocity of clean air flowing through the working area 10 and the service area 20.
In FIG. 2, arrows indicate a direction of flow of the clean air. The upper and lower plenums 2 and 3 of the clean room 1 are isolated from each other by respective filters 2a for removing particles contained in the air and gratings 3a having openings through which the air passes. The amount of flow of the clean air in the working area 10 and the service area 20 may be adjusted by the sizes of the filters 2a, the number of gratings 3a and/or the number of openings formed in the gratings 3a. 
As described above, since more air flows into the working area 10 than into the service area 20 and the working area 10 is maintained at a pressure higher than the service area 20, the air flows from the working area 10 to the service area 20. The air flow between the working area 10 and the service area 20 occurs via a wall 4 which isolates the working area 10 and the service area 20 from each other.
The wall 4 between the working area 10 and the service area 20 includes a plurality of members having gaps 4a large enough to allow the air to flow therethrough. Thus, some of the clean air flowing in the working area 10 of the clean room spontaneously flows to the service area 20 through the gaps 4a in the wall 4. The air flows between a wafer process area 31 where a predetermined process is performed on a wafer, and a wafer transfer area 32 where wafers are loaded/unloaded to/from the wafer process area 31.
An opening or a boat gate 4b for ingress or egress of a boat having a plurality of wafers mounted thereon is provided between the wafer transfer area 32 and the working area 10. An opening or a wafer gate 32a for ingress or egress of wafers is provided between the wafer process area 31 and the water transfer area 32. Doors for opening/closing the gates 4b and 32a are provided in the gates 4b and 32a. Gaps which allow a flow of air are present around the doors of the gates 4b and 32a. 
According to the above-described structure, the air flows inside the process region 30. In particular, clean air is induced from the working area 10 maintained at a high pressure, to the wafer transfer area 32 through the gaps of the boat gate 4b or other openings present in the process region 30. The clean air induced into the wafer transfer area 32 penetrates to the wafer process area 31 through the wafer gate 32a. Then, the clean air induced to the wafer process area 31 is exhausted to the service area 20 through openings present around the wafer process area or a gap 31a. As described above, the flow of air inside the process region 30 occurs due to a pressure difference between the working area 10 and the service area 20.
As shown in FIG. 3, an air-supplying device 50 for supplying purified clean air to the wafer process area 31 and the wafer transfer area 32 may be installed in the process region 30.
Referring to FIG. 3, the air-supplying device 50 absorbs clean air from the working area 10 through an induction pipe 51, purifies the clean air physically and/or chemically and then supplies the purified clean air to the wafer process area 31 and the wafer transfer area 32 as shown by arrows 52 and 53 respectively. Alternatively, the air-supplying device 50 may be installed in the lower plenum 3 so that the air is induced therefrom, rather than from the working area 10. The flow of air supplied to the wafer process area 31 and the wafer transfer area 32 by the air-supplying device 50 is performed in a direction adapted to maintain the flow of air from the working area 10 at a higher pressure than the service area 20.
Thus, as described above with reference to FIG. 2, while purified clean air is supplied to the wafer process area 31 and the wafer transfer area 32 by the air-supplying device 50, the air also is induced from the working area 10 to the wafer transfer area 32 through the boat gate 4b. Then, air penetrates from the wafer transfer area 32 to the wafer process area 31 through the wafer gate 32a. Clean air induced to the wafer process area 31 is exhausted to the service area 20 through openings present around the wafer process area 31 or the gap 31a. 
Notwithstanding these and other improvements in systems and methods for cleaning microelectronic fabrication systems, there continues to be a need for systems and methods for further improving the cleanliness of microelectronic fabrication systems.
It is therefore an object of the present invention to provide methods and systems for cleaning microelectronic fabrication systems.
It is another object of the present invention to provide microelectronic system cleaning methods and systems that can reduce contamination of microelectronic devices.
It is another object of the present invention to provide microelectronic fabrication system cleaning methods and systems that can improve the yield of microelectronic devices.
These and other objects are provided, according to the present invention, by cleaning a microelectronic fabrication system that includes a service area, a process area in the service area where microelectronic devices are processed, and a transfer area in the service area where microelectronic devices are transferred to and from the process area, by maintaining higher pressure in the process area than in the transfer area, to thereby reduce particle flow from the transfer area to the process area. It has been found, according to the present invention, that conventional microelectronic fabrication system cleaning methods and systems can allow air to flow backward to the wafer process area. By allowing backward flow of air to the wafer process area, air may be induced from a place where a lower degree of cleanliness is maintained to a place where a higher degree of cleanliness should be maintained. Due to the backward flow of air, particles contained in the transfer area, that may be generated by the transfer system, may flow onto the wafer that is being processed in the process area. In sharp contrast, by maintaining higher air pressure in the process area than in the transfer area, the present invention can reduce and preferably eliminate particle flow from the transfer area to the process area.
According to other aspects of the present invention, the microelectronic fabrication system further includes a working area that is coupled to the service area and wherein the transfer area is also coupled to the working area. Higher air pressure may be maintained in the transfer area than in the working area, to thereby enhance particle flow from the transfer area to the working area. Moreover, higher air pressure may be maintained in the process area than in the service area outside the process area, to thereby enhance particle flow from the process area to the service area outside the processor. Air flow also may be induced from the working area into the transfer area and into the process area, to maintain higher air pressure in the process area than in the transfer area. Air also may be exhausted from the transfer area to the working area, to thereby enhance particle flow from the transfer area to the working area. Air also may be exhausted from the transfer area to the lower plenum, to thereby enhance particle flow from the transfer area. Improved systems and methods for cleaning microelectronic fabrication systems thereby may be provided.